1 \input texinfo @c -*- texinfo -*-
3 @settitle Developer Documentation
5 @center @titlefont{Developer Documentation}
12 @chapter Developers Guide
16 @item libavcodec is the library containing the codecs (both encoding and
17 decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
19 @item libavformat is the library containing the file format handling (mux and
20 demux code for several formats). Look at @file{ffplay.c} to use it in a
21 player. See @file{libavformat/output-example.c} to use it to generate
22 audio or video streams.
26 @section Integrating libavcodec or libavformat in your program
28 You can integrate all the source code of the libraries to link them
29 statically to avoid any version problem. All you need is to provide a
30 'config.mak' and a 'config.h' in the parent directory. See the defines
31 generated by ./configure to understand what is needed.
33 You can use libavcodec or libavformat in your commercial program, but
34 @emph{any patch you make must be published}. The best way to proceed is
35 to send your patches to the FFmpeg mailing list.
40 FFmpeg is programmed in the ISO C90 language with a few additional
41 features from ISO C99, namely:
44 the @samp{inline} keyword;
48 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
50 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
53 These features are supported by all compilers we care about, so we will not
54 accept patches to remove their use unless they absolutely do not impair
55 clarity and performance.
57 All code must compile with recent versions of GCC and a number of other
58 currently supported compilers. To ensure compatibility, please do not use
59 additional C99 features or GCC extensions. Especially watch out for:
62 mixing statements and declarations;
64 @samp{long long} (use @samp{int64_t} instead);
66 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
68 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
72 The presentation is one inspired by 'indent -i4 -kr -nut'.
73 The TAB character is forbidden outside of Makefiles as is any
74 form of trailing whitespace. Commits containing either will be
75 rejected by the git repository.
77 The main priority in FFmpeg is simplicity and small code size in order to
78 minimize the bug count.
80 Comments: Use the JavaDoc/Doxygen
81 format (see examples below) so that code documentation
82 can be generated automatically. All nontrivial functions should have a comment
83 above them explaining what the function does, even if it is just one sentence.
84 All structures and their member variables should be documented, too.
97 typedef struct Foobar@{
98 int var1; /**< var1 description */
99 int var2; ///< var2 description
100 /** var3 description */
108 * @@param my_parameter description of my_parameter
109 * @@return return value description
111 int myfunc(int my_parameter)
115 fprintf and printf are forbidden in libavformat and libavcodec,
116 please use av_log() instead.
118 Casts should be used only when necessary. Unneeded parentheses
119 should also be avoided if they don't make the code easier to understand.
121 @section Development Policy
125 Contributions should be licensed under the LGPL 2.1, including an
126 "or any later version" clause, or the MIT license. GPL 2 including
127 an "or any later version" clause is also acceptable, but LGPL is
130 You must not commit code which breaks FFmpeg! (Meaning unfinished but
131 enabled code which breaks compilation or compiles but does not work or
132 breaks the regression tests)
133 You can commit unfinished stuff (for testing etc), but it must be disabled
134 (#ifdef etc) by default so it does not interfere with other developers'
137 You do not have to over-test things. If it works for you, and you think it
138 should work for others, then commit. If your code has problems
139 (portability, triggers compiler bugs, unusual environment etc) they will be
140 reported and eventually fixed.
142 Do not commit unrelated changes together, split them into self-contained
143 pieces. Also do not forget that if part B depends on part A, but A does not
144 depend on B, then A can and should be committed first and separate from B.
145 Keeping changes well split into self-contained parts makes reviewing and
146 understanding them on the commit log mailing list easier. This also helps
147 in case of debugging later on.
148 Also if you have doubts about splitting or not splitting, do not hesitate to
149 ask/discuss it on the developer mailing list.
151 Do not change behavior of the programs (renaming options etc) or public
152 API or ABI without first discussing it on the ffmpeg-devel mailing list.
153 Do not remove functionality from the code. Just improve!
155 Note: Redundant code can be removed.
157 Do not commit changes to the build system (Makefiles, configure script)
158 which change behavior, defaults etc, without asking first. The same
159 applies to compiler warning fixes, trivial looking fixes and to code
160 maintained by other developers. We usually have a reason for doing things
161 the way we do. Send your changes as patches to the ffmpeg-devel mailing
162 list, and if the code maintainers say OK, you may commit. This does not
163 apply to files you wrote and/or maintain.
165 We refuse source indentation and other cosmetic changes if they are mixed
166 with functional changes, such commits will be rejected and removed. Every
167 developer has his own indentation style, you should not change it. Of course
168 if you (re)write something, you can use your own style, even though we would
169 prefer if the indentation throughout FFmpeg was consistent (Many projects
170 force a given indentation style - we do not.). If you really need to make
171 indentation changes (try to avoid this), separate them strictly from real
174 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
175 then either do NOT change the indentation of the inner part within (do not
176 move it to the right)! or do so in a separate commit
178 Always fill out the commit log message. Describe in a few lines what you
179 changed and why. You can refer to mailing list postings if you fix a
180 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
182 area changed: Short 1 line description
184 details describing what and why and giving references.
186 Make sure the author of the commit is set correctly. (see git commit --author)
187 If you apply a patch, send an
188 answer to ffmpeg-devel (or wherever you got the patch from) saying that
189 you applied the patch.
191 When applying patches that have been discussed (at length) on the mailing
192 list, reference the thread in the log message.
194 Do NOT commit to code actively maintained by others without permission.
195 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
196 timeframe (12h for build failures and security fixes, 3 days small changes,
197 1 week for big patches) then commit your patch if you think it is OK.
198 Also note, the maintainer can simply ask for more time to review!
200 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
201 are sent there and reviewed by all the other developers. Bugs and possible
202 improvements or general questions regarding commits are discussed there. We
203 expect you to react if problems with your code are uncovered.
205 Update the documentation if you change behavior or add features. If you are
206 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
207 maintainer(s) will review and commit your stuff.
209 Try to keep important discussions and requests (also) on the public
210 developer mailing list, so that all developers can benefit from them.
212 Never write to unallocated memory, never write over the end of arrays,
213 always check values read from some untrusted source before using them
214 as array index or other risky things.
216 Remember to check if you need to bump versions for the specific libav
217 parts (libavutil, libavcodec, libavformat) you are changing. You need
218 to change the version integer.
219 Incrementing the first component means no backward compatibility to
220 previous versions (e.g. removal of a function from the public API).
221 Incrementing the second component means backward compatible change
222 (e.g. addition of a function to the public API or extension of an
223 existing data structure).
224 Incrementing the third component means a noteworthy binary compatible
225 change (e.g. encoder bug fix that matters for the decoder).
227 Compiler warnings indicate potential bugs or code with bad style. If a type of
228 warning always points to correct and clean code, that warning should
229 be disabled, not the code changed.
230 Thus the remaining warnings can either be bugs or correct code.
231 If it is a bug, the bug has to be fixed. If it is not, the code should
232 be changed to not generate a warning unless that causes a slowdown
233 or obfuscates the code.
235 If you add a new file, give it a proper license header. Do not copy and
236 paste it from a random place, use an existing file as template.
239 We think our rules are not too hard. If you have comments, contact us.
241 Note, these rules are mostly borrowed from the MPlayer project.
243 @section Submitting patches
245 First, read the @ref{Coding Rules} above if you did not yet, in particular
246 the rules regarding patch submission.
248 When you submit your patch, please use @code{git format-patch} or
249 @code{git send-email}. We cannot read other diffs :-)
251 Also please do not submit a patch which contains several unrelated changes.
252 Split it into separate, self-contained pieces. This does not mean splitting
253 file by file. Instead, make the patch as small as possible while still
254 keeping it as a logical unit that contains an individual change, even
255 if it spans multiple files. This makes reviewing your patches much easier
256 for us and greatly increases your chances of getting your patch applied.
258 Use the patcheck tool of FFmpeg to check your patch.
259 The tool is located in the tools directory.
261 Run the @ref{Regression Tests} before submitting a patch in order to verify
262 it does not cause unexpected problems.
264 Patches should be posted as base64 encoded attachments (or any other
265 encoding which ensures that the patch will not be trashed during
266 transmission) to the ffmpeg-devel mailing list, see
267 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
269 It also helps quite a bit if you tell us what the patch does (for example
270 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
273 Also please if you send several patches, send each patch as a separate mail,
274 do not attach several unrelated patches to the same mail.
276 Your patch will be reviewed on the mailing list. You will likely be asked
277 to make some changes and are expected to send in an improved version that
278 incorporates the requests from the review. This process may go through
279 several iterations. Once your patch is deemed good enough, some developer
280 will pick it up and commit it to the official FFmpeg tree.
282 Give us a few days to react. But if some time passes without reaction,
283 send a reminder by email. Your patch should eventually be dealt with.
286 @section New codecs or formats checklist
290 Did you use av_cold for codec initialization and close functions?
292 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
293 AVInputFormat/AVOutputFormat struct?
295 Did you bump the minor version number (and reset the micro version
296 number) in @file{avcodec.h} or @file{avformat.h}?
298 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
300 Did you add the CodecID to @file{avcodec.h}?
302 If it has a fourcc, did you add it to @file{libavformat/riff.c},
303 even if it is only a decoder?
305 Did you add a rule to compile the appropriate files in the Makefile?
306 Remember to do this even if you're just adding a format to a file that is
307 already being compiled by some other rule, like a raw demuxer.
309 Did you add an entry to the table of supported formats or codecs in
310 @file{doc/general.texi}?
312 Did you add an entry in the Changelog?
314 If it depends on a parser or a library, did you add that dependency in
317 Did you @code{git add} the appropriate files before committing?
319 Did you make sure it compiles standalone, i.e. with
320 @code{configure --disable-everything --enable-decoder=foo}
321 (or @code{--enable-demuxer} or whatever your component is)?
325 @section patch submission checklist
329 Does 'make fate' pass with the patch applied?
331 Was the patch generated with git format-patch or send-email?
333 Did you sign off your patch? (git commit -s)
334 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
337 Did you provide a clear git commit log message?
339 Is the patch against latest FFmpeg git master branch?
341 Are you subscribed to ffmpeg-dev?
342 (the list is subscribers only due to spam)
344 Have you checked that the changes are minimal, so that the same cannot be
345 achieved with a smaller patch and/or simpler final code?
347 If the change is to speed critical code, did you benchmark it?
349 If you did any benchmarks, did you provide them in the mail?
351 Have you checked that the patch does not introduce buffer overflows or
352 other security issues?
354 Did you test your decoder or demuxer against damaged data? If no, see
355 tools/trasher and the noise bitstream filter. Your decoder or demuxer
356 should not crash or end in a (near) infinite loop when fed damaged data.
358 Does the patch not mix functional and cosmetic changes?
360 Did you add tabs or trailing whitespace to the code? Both are forbidden.
362 Is the patch attached to the email you send?
364 Is the mime type of the patch correct? It should be text/x-diff or
365 text/x-patch or at least text/plain and not application/octet-stream.
367 If the patch fixes a bug, did you provide a verbose analysis of the bug?
369 If the patch fixes a bug, did you provide enough information, including
370 a sample, so the bug can be reproduced and the fix can be verified?
371 Note please do not attach samples >100k to mails but rather provide a
372 URL, you can upload to ftp://upload.ffmpeg.org
374 Did you provide a verbose summary about what the patch does change?
376 Did you provide a verbose explanation why it changes things like it does?
378 Did you provide a verbose summary of the user visible advantages and
379 disadvantages if the patch is applied?
381 Did you provide an example so we can verify the new feature added by the
384 If you added a new file, did you insert a license header? It should be
385 taken from FFmpeg, not randomly copied and pasted from somewhere else.
387 You should maintain alphabetical order in alphabetically ordered lists as
388 long as doing so does not break API/ABI compatibility.
390 Lines with similar content should be aligned vertically when doing so
391 improves readability.
393 Consider to add a regression test for your code.
395 If you added YASM code please check that things still work with --disable-yasm
398 @section Patch review process
400 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
401 clear note that the patch is not for the git master branch.
402 Reviews and comments will be posted as replies to the patch on the
403 mailing list. The patch submitter then has to take care of every comment,
404 that can be by resubmitting a changed patch or by discussion. Resubmitted
405 patches will themselves be reviewed like any other patch. If at some point
406 a patch passes review with no comments then it is approved, that can for
407 simple and small patches happen immediately while large patches will generally
408 have to be changed and reviewed many times before they are approved.
409 After a patch is approved it will be committed to the repository.
411 We will review all submitted patches, but sometimes we are quite busy so
412 especially for large patches this can take several weeks.
414 When resubmitting patches, please do not make any significant changes
415 not related to the comments received during review. Such patches will
416 be rejected. Instead, submit significant changes or new features as
419 @section Regression tests
421 Before submitting a patch (or committing to the repository), you should at least
422 test that you did not break anything.
424 The regression tests build a synthetic video stream and a synthetic
425 audio stream. These are then encoded and decoded with all codecs or
426 formats. The CRC (or MD5) of each generated file is recorded in a
427 result file. A 'diff' is launched to compare the reference results and
428 the result file. The output is checked immediately after each test
431 The regression tests then go on to test the FFserver code with a
432 limited set of streams. It is important that this step runs correctly
435 Run 'make test' to test all the codecs and formats. Commands like
436 'make regtest-mpeg2' can be used to run a single test. By default,
437 make will abort if any test fails. To run all tests regardless,
438 use make -k. To get a more verbose output, use 'make V=1 test' or
441 Run 'make fulltest' to test all the codecs, formats and FFserver.
443 [Of course, some patches may change the results of the regression tests. In
444 this case, the reference results of the regression tests shall be modified